👷 Simplify pull request workflow triggers

[tiangolo]

Summary

• Simplify workflow pull_request event declarations by removing explicit opened and synchronize activity filters.
• Let GitHub use the default pull_request activity set, which also includes reopened.

Validation

• Parsed each changed workflow as YAML before and after the edit.
• Checked the resulting diff is limited to the pull_request trigger simplification.

AI Disclaimer

Using Codex with GPT-5.5. Reviewed manually.